The invention relates to a device for inductive detection of speed and rotational direction.
Such devices are known, for example, from DE 10 2005 029 764 A1. In a first embodiment thereof the sensor element is embodied as a Hall sensor element. Hall sensor elements are very suitable for detecting variations in a magnetic field, and are therefore frequently used for speed detection. Hall sensor elements are inexpensive to acquire and can also be used at temperatures of up to about 160° C.
Hall sensors are disadvantageous, however, in that they are sensitive to dirt particles. In the worst case, soiling can lead to the sensors failing entirely.
In accordance with DE 10 2005 029 764 A1, the sensor element can alternatively be embodied as a magneto-resistive (MR) sensor element. The sensor is inductive in another alternative embodiment. In principle, inductive sensor elements are also well suited for detecting variations in a magnetic field.
In the known inductive speed detectors, wound coils are used that, in addition to high material expense, are also associated with the definite disadvantage that they are, on average, several centimeters deep.
The following table lists a few publications that are representative of Hall sensors and inductive sensors that have been used in the past:
ApplicationnumberTitlePatent holderImageStatusPat. FamilyDE4341405Arrangement for detecting the position of rotating shaftsAB Elektronik GmbHLapsedDE design patent lapsed DE4445378Method and device for detecting the angular position of a rotating shaftAB Elektronik GmbhLapsedEP; JP; US; WO DE10114858Crankshaft sensor ICAB Elektronik GmbHLapsedDE design patent registered and pending DE2847522Inductive transducer and evaluation circuit for sameRobert Bosch GmbHLapsedJP; FR DE2939643Inductive speed or angle of rotation transducerRobert Bosch GmbHLapsedGB; FR; IT DE3242109Device for detecting the speed of a rotating partRobert Bosch GmbHDE LapsedEP; JP; US all had to lapse DE4431640Sensor arrangement for determining the speed of a moving componentRobert Bosch GmbHLapsed—
A digital inductive sensor for linear position determination, angle measurement, and speed measurement having tooth-shaped pulse wheels is known from the pamphlet “Digital Inductive Position, Speed, and Direction Sensor PO120”, pages 1 through 3. The measurement coils described therein are flat and resistant to oil, water, dust, and in magnetic fields. According to the transformer principle, the sensor chip includes a transmitter coil and two receiver coils. The receiver coils are offset in the direction of movement of the pulse wheel (of the target). The possible distance between target and sensor chip is also limited in this arrangement.
The object of the invention is to overcome the problems of the prior art, i.e., to provide an arrangement for inductive speed detection that is not sensitive with respect to soiling by particles, that enables shallow installation depth, and that permits a great distance to the generator.
The tacho generator should also withstand high temperatures and high pressures such as, for example, is encountered in a transmission.